The left-hander does not have any structural damage in his throwing shoulder, but needs more time to build up strength.
"I haven't been on the mound for a while, so it takes time to get everything adjusted again and to get in that pitching mode again," Santana said Friday. "It takes time. It's not a setback at all. It just needs time to build up."
General manager Sandy Alderson said the 33-year old left-hander is expected to pitch in an exhibition game sometime from March 10-12 instead of March 2. Mets manager Terry Collins said he would like to see Santana make four exhibition starts, increasing his pitch count from 45 to 95 pitches in his spring training finale ahead of New York's April 1 opener against San Diego.
"I'm not concerned about it," Collins said. "We have some tentative dates in mind for when he can throw."
After watching Santana throw this week, Collins said he immediately knew that Santana didn't have the arm speed or feel for his pitches that he did at this time last year.
"As we started getting everything ready for the games, it's just going to take a little time," Santana said. "I feel fine, but I've just got to build up my strength in my shoulder and do a little more play catch and throw long toss to be able to go on the mound.
"To have the games right away and be ready for games, it's going to take longer. We're not trying to rush anything. We're just going to go one step at a time and just wait until the arm feels good and the shoulder feels good in order to go into games."
Alderson said he didn't think Santana will miss the start of the regular season, but said it was a possibility.
"There's no structural issue," Alderson said. "He'll be long-tossing before he gets back on the mound. We expect that his schedule will have been delayed somewhat."
A two-time AL Cy Young Award winner, Santana missed 2011 following shoulder surgery and went 6-9 with a 4.85 ERA in 21 starts last year, when he pitched the first no-hitter in Mets history on June 1 against St. Louis. He didn't pitch after Aug. 17 because of lower back inflammation.
Santana threw off a mound Sunday for the first time since August on Sunday. He said he felt fine after the 20-pitch session and was on track to start the April 1 opener against San Diego.
Mets medical director Dr. David Altchek examined Santana this week.
"We expected he would have had a normal offseason and he did have a normal offseason with the exception of not throwing," Alderson said. "His throwing program is somewhat behind, but the important thing is Altchek saw him yesterday. There's no structural issue. There's no shoulder issue, it's just an overall conditioning issue as it relates to throwing."
Santana gets $25.5 million this year in the final guaranteed season of his $137.5 million, six-year contract. The Mets hold a $25 million option for 2014 with a $5.5 million buyout.
Alderson also said reliever Pedro Feliciano and outfielder Jamie Hoffmann have returned to New York for follow-up exams to their physicals, which took place Sunday. Alderson would not go into detail other than terming the issues "non-orthopedic." He expects the both players to return to camp within two days.
New York said reliever Frank Francisco is expected to begin throwing Monday or Tuesday. Francisco was examined by Altchek on Thursday and Alderson said it was determined there was no structural issues in his surgically repaired right elbow. Francisco has not pitched in more than a week due to inflammation.